Thermolytic conversion of hydrocarbon gases to liquid



May 17, 1938. J. w. THROCKM'ORTON THERMOLYTIC CONVERSION OF HYDROCARBON GASES TO LIQUID Filed July 23, 1937 INVENTOR John W T hrac/rmorton BY 2 F ATTORNEY Patented May 17, 1938 PATENT OFFICE THERMOLYTIC CONVERSION OF HYDRO- CARBON GASES LIQUID John W. Throckmorton, New York, N. Y., as-

signor to The Pure 01! Company, Chicago, 111.,

a corporation of Ohio Application July 23, 1937, Serial No. 155,152

12 Claims.

Y Thisinventionrelates to method and apparatus for converting hydrocarbon gas to liquid hydrocarbons and is more particularly concerned with method and apparatus for efficiently converting hydrocarbongas mixtures into gasoline type hydrocarbons. i

In theoperation of thermolytic gas polymerizationprocesses it is difficult to obtain complete conversion of thereactable constituents in a one stepsystem without the necessity of high recycle ratios. But high recycle ratios mean low throughput with resultan't low output and high operating cost.

In accordance with this invention the charging gas is fractionated so as to separate the C2 hydrocarbons and lighter gas from a fraction containmg C: and heavier hydrocarbons. The latter fraction is charged through suitable heating and reaction zones separate from the light fraction, wherein it is subjected to suitable conditions of time, temperature and pressure to convert a substantial portion togasoline boiling hydrocarbons.

'Ihelight fractionjmay or may not be further fractionated to remove the lightest constituents suchas hydrogen and methane, and then charged toaseparatecracking coil preferably operated at higher temperatures and lower pressures than we coil to whichjtheh'eavy fraction is charged.

In t e'cracking'co conversion of gas to liquids' and, to olefins takesffplace. The desirable portions ofjthereajcte gas are absorbed in a liquidoil mnscmu fap the rich oil used to chill the reaction produetsf-froin the high pressure coil. Thefcombined prtxluct's are then fractionated and the resultinglgas mixed with the fresh charge. In this mannerg the desirable portions ofthe gasesfromthereaction zone are recovered and mixed withfthe fresh gas after elimination of the iixed gas lowin polymerizable constituents,, ifrom the systenigiandf a] uniform blend of finished gasoline'is obt "t ed all in a single opi ifln- By ajjtw o "step op'eration of the type above described'therecycle in the high pressure coil may be maintained between the limits of lefgastolf part of fresh gas, H i recycle ratio in the low pressurefcoil: 1 Moreovergthe yse of the two step systemenables" themaintenance of optimum conditionsfor the productscharged to each coil, resultingin longe'frim'sTwitheutexcessive coke formation. The throughput andjgasoline yield are greatly augmentemand operating costs are correspondingly ideci'eased be eause of lower overheadi In order to more fully comprehend the nature and scope of the invention, reference, should be had to the following description together with the accompanying drawing of which The single figure is a diagrammatic elevational 5 view of apparatus suitable for carrying out the invention.

Referring to the drawing, the numeral l indicates a line through which fresh gas is charged to the system by means of pump or compressor 3. The charging gas may be natural or cracked gas, gas from a liquid or vapor phase 011 cracking operation, or other gas containing a. substantial amount of Cs and C4 hydrocarbons. The charging gas is then pumped through line 5 and cooler l to gas and liquid separator 9. If the charge is gaseous it may be compressed in compressor 3 to a pressure of approximately 150-350 pounds per square inch and cooled to a temperature of -100 F. before entering the gas separator. If the charge is liquid, the samecondltions of temperature and pressure should be maintained.

The liquid fraction consisting chiefly of C: and C4 hydrocarbons is withdrawn from the lower part of the gas separator through line I I by means of pump l3, and may be charged through line I 5 controlled by valve II, to the inlet of coil l9 located in furnace 2| at a pressure ranging from 200-3000 or more pounds per square inch.

The pressure, under which the charge to the. coil I9 is maintained, will depend largely upon the composition of the charge and upon the product desired. If the charge contains substantially only saturated hydrocarbons, pressures of approximately atmospheric to 250 pounds per square inch and temperatures of approximately l200-1300 F. will be preferably maintained with a short reaction period in order to convert the saturated hydrocarbons to unsaturates. In such case the products, after leaving the heating coil, may be chilled at 23 by means of a portion of the fresh charge which is by-passed through line 26 controlled by valve 21 to a temperature of approximately 10'751200 F. and then passed to a reaction coil or chamber 29 maintained under substantially the same pressure as the cracking coil, wherein the products are given suflicient time to polymerize to hydrocarbons boiling within the gasoline range. The reaction coil 29 is preferably provided. with means for controlling temperature. For this purpose the coil or chamber may be enclosed in a suitable vessel through which a draft of air, combustion gases, or other If the charge to the coil I9 contains approximately 20% or more of oleflnic hydrocarbons, it may be heated in the coil I9 to a temperature between approximately 800-l050 F. under pressure of 500-3000 or more pounds per square inch, and these temperature and pressure conditions maintained in the reaction coil; or if it is desired to produce primarily aromatic hydrocarbons, the charge may be maintained under a pressure of approximately atmospheric to 250 pounds per square inch and at temperatures of 1075-12oo F.

The products issuing from the reaction coil 29 may be suddenly chilled to a temperature of approximately 600 F. or lower by direct contact with an intermediate oil fraction formed in the system and which is injected into the issuing products at the point 3I. Depending upon the pressure maintained in the reaction coil, the pressure on the reaction products may or may not be reduced at the valve 33 and the products then passed into the lower portion of fractionating tower 35. The temperature of the reaction products, after chilling, should be high enough to permit fractionation thereof without additional heating.

The reaction products are separated in the fractionating tower 35 into residual oil, an intermediate fraction boiling above the gasoline range, which is collected on the plate 31, gasoline boiling hydrocarbons which are collected on the plates 39 and I, and residual gas which comes over the top of the tower through line 43. The residuum is withdrawn from the bottom of the fractionating tower through line 45 controlled by valve 41, at which the pressure is reduced to approximately atmospheric pressure, and the oil is flashed in flash tower 49 into vapors and tar. The residual tar is withdrawn from the flash tower through line 5|, by means of pump 53, through cooling coil 55, to-any suitable place of storage. The vapors are withdrawn from the flash tower through line 51 and condenser 59 into separator 6|. Any uncondensed material is withdrawn from the separator 5| through line 53, and eliminated from the system. The condensate is recycled through line 55, by means of pump 51, to an intermediate portion of the fractionating tower 35, as reflux. This reflux preferably enters the tower at a point intermediate the trays 31 and 39. v

The gasoline boiling constituents are withdrawn from the fractionating tower through line 59 controlled by valve II and line I3 controlled by valve I5 and pass through a common line 11 into a stripper I9. In the stripper light hydrocarbons, such as C: and a portion of the C4 hydrocarbons, are vaporized and taken overhead through the line 8|. The stripper I9 is preferably provided with suitable fractionating plates and heating means in order to stabilize the gasoline. The stabilized gasoline may be withdrawn from the stripper through lines 53 and and passed to storage through line 91 controlled by valve 99.

The pressure in the fractionating tower 35 is preferably maintained at approximately 175-250 pounds per square inch and the temperature at the top of the tower is maintained sufliclently low to condense the major portion of the gasoline fraction. The incondensible gases together with a small amount of uncondensed gasoline va'pors leave the fractionating tower 35 through line 53, then pass through condenser 9|, into gas and liquid separator 93. 'The condensate from separator 93 is recycled through line 95 by means of pump 91, as reflux, to the upper portion of the fractionating tower 35. The gases which remain uncondensed are withdrawn from the upper portion of the separator 93, through line 99, and join the fresh gas in the line 5, to be reprocessed.

The gases which are not liquefied in the separator 9 are withdrawn from the top thereof through line IOI controlled by valve I03 and charged to the inlet of the cracking coil I05 located in the furnace I0I. If desired, the gases withdrawn through the line I0l may be further fractionated by being by-passed through line I09, compressed by compressor III, and charged to separator I I3. In this manner the hydrogen and methane may be eliminated from the gas prior to charging to the cracking coil. The gases will be compressed in compressor III sufliciently to liquefy the C2 fractions in order to separate them from the hydrogen and methane which are eliminated from the system through line II5 controlled by valve II'I. The liquefied C2 fractions may be withdrawn from the separator II3, through line II9 controlled by valve I2I, and charged to the inlet of the cracking coil I05.

When the gases charged to the cracking coil I05 are not further fractionated they are preferably charged thereto in the gaseousstate under pressure of from 50-100 pounds per square inch. The gases may be heated in the cracking coil to temperatures of l200-1600 F. The temperature and pressure conditions maintained in this coil I05 will be those most suitable for obtaining maximum yield of gasoline boiling hydrocarbons. If the fraction removed from separator 9 through line IN is low in oleflnic hydrocarbons, hightemperatures and low pressures, such as those above mentioned, are preferably maintained in the coil I05. If the oleflnic content of these gases is suillciently high, that is, above approximately 20%, it may be advantageous to further fractionate them to remove the hydrogen and methane, and charge the remaining gas in the liquid or gaseous phase to the coil I05. If liquid phase charging is employed, the pressures maintained in the coil I05 may be 500-3000 or more pounds per square inch and the temperatures preferably between 700 and 1000 F. If the olefin content is sufllciently high to avoid necessitating further fractionation, the gases charged to the coil I05 may be maintained at low pressures of approximately atmospheric to 250 pounds per square inch and at temperatures of approximately l-1200 F. It will be understood, however.

that these conditions of temperature and pressure may be varied in accordance with the composition of the charge to the coil. The reaction time will vary with the pressure and temperature conditions maintained. Generally the reaction time will vary directly with the pressure and inversely with the temperature.

In the coil I05 cracking and/or polymerization of the gases take place in the formation chiefly of liquid hydrocarbons and olefinic gases. The reaction products issue from the cracking coil through the line I23 and are suddenly chilled by direct contact with an intermediate condensate formed in the process, which is introduced into the line I23 at the point I25.- The partially chilled reaction products are further cooled by passing through the cooling or condensing coil I21, and then pass through line I29 controlled by valve I3I, into gas and liquid separator I33. From the separator I33 any liquid products are withdrawn through the line I35 by means of 75 pump I 31. The gases are withdrawn by means of the compressor I39 through line Ill and cooling coil I43 and charged to the lower portion of the absorber I45.

Intermediate condensate substantially boiling within the range of gas oil is withdrawn from the fractionating tower 35 through line I" by means of pump I49 and passes through cooling coil Iii.

iii to the line I23 where it is injected into the reaction products from the coil I in order to cool these products below reaction temperature. The remaining portion of the condensate passes through line I51 controlled by valve I59 into the upper portion of absorber I45 wherein it passes counter-currently to the gases entering the bottom of the absorber. The pressure in the absorber may be preferably between 175225 pounds per square inch and the temperature approximately 75-100 F. Under these conditions of temperature and pressure substantially all the Ca and heavier hydrocarbons will be absorbed as well as a substantial portion of the C: hydrocarbons, mainly ethylene. The hydrogen, methane and the main portion of the C2 hydrocarbons are eliminated from the absorber and from the system through line IGI controlled by, valve I63.

Rich oil leaves the bottom of the absorber through line I65 and is charged by pump I61 through line I69 into line. I'll. The liquid hydrocarbons from the separator I33 join the rich oil in the line I60. I'he stream of rich absorber oil together with the liquids from separator I 33 may be split in the line ill, a portion passing through valve I13 and entering the line 30 at the point iii in order to chill the reaction products below reaction temperature, and another portion passing through the valve I15 into the intermediate portion of the fractionating tower above the plate 31 to act as reflux. i

In the fractionating tower the absorber oil is stripped of its gases which pass over from the tower through line 43 and are processed as heretofore described.

By virtue of the fact that substantially all the C2 and lighter gases. are eliminated from the charge to the coil I9, the recycle ratio to this coil is kept low allowing for a greater throughput of fresh charging stock. Moreover, the elimination of these light gases permits the maintenance of those conditions in the coil I9 and reaction coil'29 which will produce the maximum amount of desired product. The C2 and lighter fractions, after having been subjected to a combined cracking-polymerization operation, or to polymerization alone, in the coil I05, are substantially eliminated from the system through the line I6I, only a relatively small portion thereof being absorbed in the absorber and recycled to the system.

What is claimed is:

1. The process of converting gas mixtures, containing chiefly C2, C3 and C4 hydrocarbons, to liquid hydrocarbons which comprises separating the mixture into a fraction containing chiefly Ca and C4 hydrocarbons and another fraction containing C2 hydrocarbons and lighter gases, subjecting each fraction in a separate zone to suitable conditions of time, temperature and pressure for converting the gaseous constituents to liquid hydrocarbons boiling within the gasoline boiling range, separating the bulk of the C2 and lighter gases from the reaction products of the together with the reaction products of the C1. C4

hydrocarbons. separating the incondensible gases from the normally liquid hydrocarbons, and uniting the incondensible gases with the fresh gas From the cooling coil Iii a portion of the condensate passes through line I53 and valve prior to separation thereof into fractions. 2. .The process of converting gas mixtures, containing chiefly C2, C: and C4 hydrocarbons, to liqfraction conversion into liquids and gases, con-.-

taoting the gases imder pressure with absorber oil in order to absorb the major portion of the C3 and C4 hydrocarbons, charging richabsorber oil into a common fractionating zone with the reaction products of the C3, C4 fraction, separating normally gaseous hydrocarbons from the normally liquid hydrocarbons in said fractionating zone, and mixing the normally gaseous hydrocarbons with fresh gas prior to separation thereof. into fractions.

3. Process in accordance with claim in which the rich absorber oil is used to chillthe reaction products of the C3, C4 fraction below conversion temperature, and the chilled mixture charged to the common .fraotionating zone.

4. Process in accordance with claim 2 in which the liquid reaction products from the conversion of the C2 andlighter gases are charged to the common fractionating zone.

5. Process in accordance with claim 2 in which acondensate heavier than gasoline is withdrawn from the fractionating zone and cooled, and a portion of the cooled condensate used to chill the reaction products of the C2 and lighter gases below reaction temperature and another portion used as the absorption menstruum.

6. Process in accordance with claim 2 in which the gas mixture charged to the process contains a substantial proportion of C3 and C4 olefins, and in which the C3, C4 fraction is subjected to conversion at temperatures of 800-1050 F. and at pressures above 500 pounds per square inch while the C2 and lighter gas fraction is subjected to conversion at temperatures between 1200" and 1600 F. and under pressures below 100 pounds per square inch.

'7. Process in accordance with claim 2 in which the gas mixture charged to the process is rich in olefins and in which the fraction containing the lighter gases is further fractionated to remove methane and hydrogen, and the remainder of the fraction is subjected to temperatures between 700 and 1000 F. under pressures above 500 pounds per square inch while the C3, C4 fraction is subjected to temperatures of approximately 1075-1200 F. under pressures up to approxi 500 pounds per square inch while the C3, C4 fraction is subjected to temperatures of approximately 800-l050 F. under pressures above 500 pounds per square inch.

.reaction means, means for separating normally liquid from normally gaseous constituents in said cooled products, means for contacting said gaseous constituents with absorber oil under such conditions as to absorb substantially only the heavier portions of said gaseous constituents, means for eliminating the unabsorbed constit-' uents from the system, means for contacting the rich absorber oil with the hot reaction products from said second reaction means in order to partially cool said products, means for fractionating the partially cooled products in order to separate the normally gaseous from the normally liquid constituents, and means for uniting the last mentioned normally gaseous constituents with the fresh gases charged to the system.

10. Apparatus in accordance with claim 9 including means for charging a portion of said rich absorber oil directly to said fractionating means.

11. Apparatus in accordance with claim 9 including means for collecting heavy condensate in said fractionating means, means for withdrawing said heavy condensate and contacting a portion thereof with hot reaction products from said heatingand reaction means, and means for charging another portion of said condensate to said absorption means.

12. The process of converting gas mixtures, containing chiefly C2, C3 and C4 hydrocarbons, to liquid hydrocarbons, which comprises separating the mixture into a fraction containing chiefly Ca and C4 hydrocarbons and another fraction containing C2 hydrocarbons and lighter gases, subjecting each fraction in a separate zone to suitable conditions of time, temperature and pressure for converting thegaseous constituents to liquid hydrocarbons boiling within the gasoline boiling range, separating the bulk of the C: and lighter gases from the reaction products of the lighter gases and eliminating them from the system, charging separated normally gaseous andnormally liquid reaction products resulting from said conversion oi the lighter gases to a common fractionating zone together with the reaction products of the C3, C4 hydrocarbons, separating the incondensible gases from the normally liquid hydrocarbons, and uniting the incondensible gases with the fresh gas prior to separation thereof into fractions.

JOHN W. THROCKMORTON. 

